The present invention relates to variable displacement compressors which can vary displacement by changing the crank chamber pressure.
FIG. 5 shows a swash plate type variable displacement compressor used in automobile air conditioners. A crank chamber 82 is formed between a front housing 80 and a cylinder block 81. A drive shaft 83,that is driven by the automobile engine is supported by the front housing 80 and the cylinder block 81. A lug plate 84 that rotates integrally with the drive shaft 83 is arranged inside the crank chamber 82. A swash plate 85 is connected to the lug plate 84 through a hinge mechanism 102.
A plurality of cylinder bores 86 are formed in the cylinder block 81. Each cylinder bore 86 is arranged at equal intervals about the axis of the drive shaft 83. Pistons 87 are housed inside the cylinder bores 86. When the drive shaft 83 is driven, the swash plate 85 rotates and each piston 87 connected to the swash plate 85 reciprocates inside the associated cylinder bore 86 between a top dead center position and a bottom dead center position. The swash plate 85 converts the rotation of the drive shaft 83 to a reciprocating motion of the piston 87. The displacement is varied by the stroke of the piston 87, which changes in response to the inclination angle of the swash plate 85.
A valve plate 88 is located between the cylinder block 81 and a rear housing 89. A suction chamber 90 and a discharge chamber 91 are located in the rear housing 89. The reciprocating motion of each piston 87 causes refrigerant gas to be drawn into the cylinder bore 86 from the suction chamber 90 and discharges the refrigerant gas, which is compressed in the cylinder bore, into the discharge chamber 91.
The inclination angle of the swash plate 85 and the stroke of the pistons 87 are determined by the pressure (crank pressure) inside the crank chamber 82 and the pressure inside the cylinder bore 86. The displacement of the compressor is varied by changing the inclination angle of the swash plate 85 or, in other words, the stroke of the pistons 87.
The pressure in the crank chamber 82 is varied in response to the difference between the flow rate of refrigerant gas flowing into the crank chamber 82 from the discharge chamber 91 and the flow rate of refrigerant gas flowing out from the crank chamber 82 to the suction chamber 90. A pressurizing passage 92 connects the discharge chamber 91 and the crank chamber 82 by way of an electromagnetic control valve 93. The electromagnetic control valve 93 controls the amount of refrigerant gas flowing into the crank chamber 82 through the pressurizing passage 92. A bleed passage 94 connects the crank chamber 82 and the suction chamber 90. Refrigerant gas inside the crank chamber 82 constantly flows into the suction chamber 90 through the bleed passage 94.
The control valve 93 opens fully when de-excited. This maximizes the flow rate of refrigerant gas entering the crank chamber 82 through the pressurizing passage 92. When the control valve 93 is excited, the control valve 93 closes in accordance with the level of an electrical current supplied to the control valve 93. This restricts the flow rate of refrigerant gas flowing from the discharge chamber 91 to the crank chamber 82.
A lip seal 95 is used to seal the space between the drive shaft 83 and the inner wall surface of the front housing 80. The end of the drive shaft 83 extends to the outside of the housing. An electromagnetic clutch 96 is fixed to the end of the drive shaft 83. The electromagnetic clutch selectively transfers the drive power of the engine E to the drive shaft 83.
A thrust bearing 97 is located between the lug plate 84 and the front housing 80. The end of the drive shaft 83 is supported in a bore 98. A support spring 100, which is a compression spring, is located between a retaining ring 99 that is located inside the bore 98 and the end of the drive shaft 83. The support spring 100 applies axial force to the drive shaft 83 in a direction towards the front housing 80 (to the left in FIG. 1). Further, the support spring 100 eliminates slack in the axial direct-ion of the drive shaft 83.
The swash plate 85 is at its maximum inclination angle position when it makes contact with the lug plate 84 and is at its minimum inclination angle position when it contacts a stopper ring 101 that is fixed to the drive shaft 83.
When the engine E is stopped, the control valve 93 fully opens and the refrigerant gas flows inside the crank chamber 82 through the pressurizing passage,92. There is a chance that the crank pressure at this time may temporarily increase to an excessively high value. If this occurs, the swash plate 85 (indicated by the broken lines in FIG. 5) presses against the stopper ring 101 with excessive force when it reaches the minimum inclination position. Further, the swash plate 85 pulls the lug plate 84 rearward (to the right in FIG. 1) through a hinge mechanism 102. As a result, the drive shaft 83 will move axially rearward against the support spring 100.
When the automobile accelerates, the displacement of the compressor is reduced to reduce the load of the compressor on the engine E. To accomplish this, the control valve 93 is fully opened and refrigerant gas in the discharge chamber 91 suddenly flows to the crank chamber 82. Therefore, the crank pressure may temporarily increase to an excessively high level, which applies a rearward force to the drive shaft 83.
If the crank pressure increases excessively in this manner, the drive shaft 83 will move rearward in the axial direction. This causes the pistons 87 to move to a position that is closer to the valve plate 88. Consequently, there is a possibility that the head of each piston 87 may strike the valve plate 88 when reaching the top dead center position. This will produce striking noises or vibrations and will damage the pistons 87 and the valve plate 88.
If the drive shaft 83 moves rearward, a movable clutch plate 96a of the electromagnetic clutch 96 will also move rearward. Because of this, the movable clutch plate 96a and a fixed clutch plate 96c make contact even if a magnetic coil 96b is demagnetized. As a result, friction occurs between the clutch plates 96a, 96c leading to noise and heat generation.
Moreover, if the drive shaft 83 moves rearward, the axial position of the drive shaft 83 changes relative to the lip seal 95, which is supported on the front housing 80. Normally, the drive shaft 83 makes contact with the lip seal 95 at a predetermined axial position,. Foreign matter, such as sludge, is adhered to the outer surface of the drive shaft 83 at locations other than the predetermined axial position. Thus, if the axial position of the drive shaft 83 changes relative to the lip seal 95, sludge gets caught between the lip seal 95 and the drive shaft 83. This reduces the sealing performance of the lip seal 95 and causes gas leaks from the crank chamber 82.
In order to solve this problem, increasing the compressive force of the support spring 100 such that the drive shaft 83 does not move rearward even if the crank pressure increases to an excessively high value has been considered. However, this increases the load applied to the thrust bearing 97. Consequently, friction between the thrust bearing 97 and the front housing 80 increases, which shortens the life of the compressor, increases power loss, and decreases the compression efficiency.
The object of the present invention is to provide a variable displacement compressor that restricts axial movement of the drive shaft and enables each compressor member to function properly.
To achieve the above object, the present invention provides a compressor including a housing, a crank chamber defined in the housing, a drive shaft arranged in the housing and supported by the crank chamber, a cylinder bore extending through the housing, and a piston accommodated in the cylinder bore. A drive plate is connected to the piston to convert a rotation of the drive shaft to a reciprocating motion of the piston. The drive plate inclines relative to the axis of the drive shaft between a maximum inclination position and a minimum inclination position in accordance with the pressure of the crank chamber. A retainer surface is arranged in the housing and extends substantially perpendicular to the axis of the drive shaft. A restricting mechanism is arranged between the drive plate and the retainer surface. The restricting mechanism receives the drive plate and restricts movement of the drive plate when the inclination of the drive plate decreases.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.